Layer shifting is when an axis loses position mid-print and every layer after that point is offset from the layers below. It looks dramatic but almost always traces back to one of four causes: a belt that's too loose (or too tight), a stepper driver that thermal- throttled, acceleration that's beyond what the printer can deliver, or a physical collision the printer couldn't recover from.
If the shift is in one axis only , it's almost always that axis's belt or pulley. Power off, manually move the head along that axis, and feel for tight spots, loose belt slack, or a pulley set screw spinning on the motor shaft. Re-tension the belt, tighten the grub screw onto the flat of the motor shaft, and retry. If multiple axes shift on the same print, suspect the stepper driver(s) overheating or acceleration set too high.
Look at the print and identify which axis the shift is in:
The single most common cause. Modern printers ship with belts that loosen over the first weeks of use as the loops bed in.
See Belt tension and calibration for printer-specific procedures.
The pulley on each motor is held to the shaft by a tiny grub screw. If the screw isn't biting the flat side of the shaft, the pulley spins freely under load and you get random shifts.
Grub screws vibrate loose over time. A drop of blue threadlocker (Loctite 243) holds them indefinitely and still allows future removal.
If the print shifts consistently after ~30–60 minutes (not at the start), the stepper driver chip is probably thermal-throttling. Symptoms include:
If you've cranked acceleration in your slicer past what the printer can physically deliver, the motors will skip steps trying to keep up.
If you're using a "speed" slicer profile and seeing layer shifts, roll back to "standard" and verify acceleration values match the table.
If a layer warped upward, the nozzle can collide with it on the next pass. The motor either skips steps or pushes the part loose.
If the entire print shifts in both axes at exactly the same point: